The production of glasses is presently the occupation of a major branch of industry. This production also brings about some problems, e.g. pieces of broken glass are a by-product of all auch glass manufacturing processes. Broken pieces of glass also result from the use of glass articles. The increasing volume of discarded glass pieces renders the problem more and more serious, since the glass industry is not readily able to use these volumes for glass production again. The main difficulties result from the different chemical compositions and the contamination of the broken glass pieces. For this reason, attempts have been made to re-use this glass waste, and thus promote the utilization of this valuable raw material reservoir. As known the literature, the glass waste is considered to be inferior material. Glass waste is used with more or less success e.g. as an additive for asphalt and cement and for the production of glass-clay bricks, foam glasses, glass wool, etc. Because the issue of raw material resources is coming more and more into the foreground and because of the problems of ecology, the need to use glass waste is becoming more and more a necessity.
In the production of glass, soda (Na.sub.2 CO.sub.3) is one of the most costly materials. The production of soda alone in large quantities is not a raw material problem it is produced from sodium chloride. But as a by-product of this production, CaCl.sub.2 is produced, for which up to now hardly any use has been found. Consequently, it is desirable to recover the alkali from waste glass. The present invention discloses a process for the treatment of broken glass pieces, wherein by a hydrothermal, alkaline disintegration of the glass on the one hand recovery of alkali is achieved and on the other hand materials having a large specific surface are obtained.
The production of alkali silicate solutions by a disintegration of SiO.sub.2 materials with NaOH solutions is known in the art. By means of such wet processes, water glass of high purity is also produced. The use of different materials which are not composed of SiO.sub.2 exclusively brings about difficulties, however. The yield of SiO.sub.2 is low, because either there are small amounts of soluble silicates from the start soluble silicates are formed during the process. It is, for instance, known that disintegration with NaOH solution is used for perlite rock and nepheline syenites, wherein next to the alkali silicate solution a residue of aluminosilicate nature is produced. In some instances after various treatments products having an increased alkali-soluble SiO.sub.2 content are obtained.
One possibility is for insstance, to provide, as a first step, a maceration. Serpentines may also be used for the production of water glass. A process is also known wherein alkali- and alumina-containing rocks are melted, quenched, and macerated with acid and then subsequently are treated with NaOH solution in order to produce an alkali silicate solution.
It will thus be appreciated that the economical disintegration of SiO.sub.2 -containing materials with NaOH solutions depends on what yield is possible. This determines what starting materials are used or what pretreatment is required. When the usual alkali silicate glasses are to be judged under this aspect, it has to be considered that the alkali earth content shares the second and third place with the alkali proportion in the composition. Under hydrothermal, alkaline conditions, low-soluble calcium hydro silicate phases can form. In this way, SiO.sub.2 can be dissolved only in a limited amount.